CHANDRAPUB - Chandra Public Observations
This database table contains all of the archived observations made by the
Chandra X-Ray Observatory (CXO, formerly known as the Advanced X-ray
Astrophysics Facility or AXAF) that are available to the public.
The HEASARC constructs this database table on a twice-weekly basis by
querying the database table at the Chandra X-Ray Center (CXC) website, as
discussed in the Provenance section. Data products stored at the CXC can be
accessed through the Browse Web interface using this database table.
The PVC phase was during the first few months of the CXO mission; some of the
calibration observations that are for monitoring purposes will be performed
in later mission cycles. All calibration data (entries with Type = CAL in
this database) are placed immediately into the CXO public data archive at the
Chandra X-Ray Observatory Center (CXC); please see the Web page at
http://asc.harvard.edu/ for more information on the CXC data archive). GTO
observations during Cycle 1 or any subsequent Cycle will probably occupy 100%
of months 3-4, 30% of months 5-22, and 15% of the available time for the
remainder of the mission. Guaranteed Time Observers will have the same
proprietary data rights as General Observers (i.e., their data will be placed
in the public CXC archive 12 months after they have received the data in
For detailed information on the Chandra Observatory and datasets see:
http://cxc.harvard.edu/ for general Chandra information
http://cxc.harvard.edu/cda/ for the Chandra Data Archive
http://cxc.harvard.edu/cal/ for calibration information
http://cxc.harvard.edu/caldb/ for the calibration database
http://cxc.harvard.edu/ciao/ for data analysis
http://cxc.harvard.edu/ciao/download/ for analysis software
http://cxc.harvard.edu/ciao/threads/ for analysis threads
http://cda.harvard.edu/chaser/ for WebChaSeR
The Chandra X-Ray Center (CXC) website at http://cxc.harvard.edu/ is the
source of the information in this table and the associated data products.
The HEASARC constructs this database table on a twice-weekly basis
based on information obtained from the Chandra Data Archive at the CXC
web site. This version of the CHANDRAPUB database table has fewer entries
than the original version because a number of observations which were
either canceled or discarded have been removed.
Links to the CXC data archive are accessible through the Browse Web interface
for table entries where the status is 'archived'. The current links allow the
user to select Chandra data products in one of two ways:
(i) select a set of files, either all (but Level 0), and/or Intermediate
Level 1/1.5, and/or Level 2 processed data products, and then create a TAR
file at the CXC for immediate or later download. This is done via a cgi-bin
query of the Chandra Data Archive (CDA) Provisional Data Retrieval Interface
at the CXC. The various links for a given observation will all point to the
same page, but different subsets of the full archival data for the
observation will be presented there for selection. The TAR file is created at
the CXC, and separate TAR files must be created for each observation. Using
this method, there is no way to combine data retrieval from multiple
observations (although this capability is available via a direct WebChaSer
query at http://cda.harvard.edu/chaser/), or to combine the retrieval of
Chandra data with data from other missions.
(ii) select the data products that are available in the Chandra Data Archive
(CDA) anonymous FTP area. These product categories are more detailed than for
option (i) and include the observation summary file, the V&V Report, images
and source lists (both FITS and JPEG), events lists, orbital ephemeris abd
aspect solution files, gain plots, spectra, bad pixel lists, and
miscellaneous files. Using this method, the TAR file is created on the fly,
and data from multiple observations can be retrieved together.
A unique Chandra Observation Identifier.
The name of the target of the observation.
The Right Ascension of the target in the selected equinox.
The Declination of the target in the selected equinox.
The Galactic Longitude of the target.
The Galactic Latitude of the target.
The start time of the observation (UTC).
The detector requested for the exposure. There are 2 focal-plane
scientific instruments, the AXAF CCD Imaging Spectrometer (ACIS) and the High
Resolution Camera (HRC). The ACIS has 2 arrays of CCDs: the ACIS imaging
array (ACIS-I) is optimized for imaging wide fields, while the ACIS
spectroscopic array (ACIS-S) is optimized for grating spectroscopy and for
imaging smaller fields. The HRC consists of 2 microchannel plate array which
are used as the primary detection devices: the HRC-I is optimized for direct
imaging, while the HRC-S is optimized for imaging the dispersed flux from the
Low Energy Transmission Grating (LETG). Thus, there are 4 possible detectors:
ACIS-I, ACIS-S, HRC-I, and HRC-S.
The grating setting requested/used for the exposure. There are two
objective transmission gratings: the High Energy Transmission Grating (HETG)
and the Low Energy Transmission Grating (LETG). The ACIS-S detector is normally
used to read out the HETG spectra, while the HRC-S detector is normally used
to read out the LETG spectra. Thus, there are 3 possible grating selections:
LETG, HETG, and NONE (i.e., no grating requested).
The requested or actual exposure time, in kiloseconds.
The type of observation. There are five general types of target:
those accepted in a General Observer (GO) proposal (type = 'GO'), those
accepted in a Guaranteed Time Observing (GTO) proposal (type ='GTO'), those
used for a Calibration observation (type = 'CAL'), those accepted as Targets
of Opportunity (type = 'TOO'), and those observed as Director's Discretionary
Time (type = 'DDT'). Please note that some DDT targets may have been
designated as TOO targets.
The last name of the assigned Principal Investigator (PI) for the
observation. Notice that this is not
always an unambiguous identifier, since there are a number of last names
(e.g., Drake and White) which are shared by more than one astronomer. If
in doubt, it is recommended that the target lists at
http://cxc.harvard.edu/target_lists/ be consulted for the full PI name for
all accepted proposals.
The cycle number in which the proposal to observe the particular
target was submitted. Note that any observations which the CXC have not
assigned proposal numbers have been defaulted to a value of 0 for this
parameter in this HEASARC database.
The proposal number to which the target corresponds as
assigned by the CXC.
The public release date for this dataset.
The sequence number to which the observation corresponds
(assigned by the CXC).
The operational mode of the detector. For ACIS it is of the form Ty_xxxxx or
CC_xxxxx, where y is an uppercase letter and x is a hexadecimal digit; Ty
indicates timed exposure, CC continuous clocking. For HRC it will be DEFAULT
for most observations.
The subject category of the observation, as assigned by the CXC.
The Browse Object Classification, as derived from the Category
parameter provided by the CXC. Note: This is done through a rather crude
mapping. Some of the assigned classes will be incorrect. E.g., observations
assigned to the isolated neutron stars and supernovae category will be mapped
to the supernova remnant Browse object class, since all three are grouped in
one Chandra category.
Questions regarding the CHANDRAPUB database table can be addressed to the
HEASARC User Hotline.
If you have any problems, please consult the help
page or mail firstname.lastname@example.org